Operation of an extended pressure range (XPR) miniature residual gas analyzer at millitorr pressures allows direct measurement of process gases involved in physical vapor deposition without the need for pressure reduction and associated pumps. A new electron multiplier (EM) capable of sustained operation at all XPR operating pressures (up to 20 mTorr) extends the measurement speed at process pressure while maintaining nanoTorr detection limits at base pressure. Design features that allow the EM to operate continuously at high pressures are presented together with data that shows that a gain of 100 is optimum for practical measurements of gas species from 10@super -9@ to 10@super -2@ Torr. A comparison of the operation of the XPR with a standard RGA shows each instrument has a similar dynamic range of ion currents but the pressures producing the currents are shifted two decades of pressure higher for the XPR. The physical phenomena of ion-molecule reactions do occur at millitorr pressures but do not interfere with useful measurements of the impurities in Ar sputtering gases or the detection of contaminants (like photoresist) in degas chambers. Examples are given of ion molecule reactions, e.g. N@sub 3@@super +@ and Ar@sub 2@@super +@ produced at pressures of 10 mTorr for N@sub 2@ and Ar, respectively.